Inhibitory and disinhibitory circuit motifs in the deep cerebellar nuclei

• Applicant: Dr. Christine Pedroarena
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 519121964

Normal patterns of brain activity depend crucially on inhibition. Therefore, how exactly inhibition shapes neural activity is intensely studied. Inhibitory neurons (INs) exert their actions by forming part of at least two kind of inhibitory circuits: feedforward and feedback motifs. However, if inputs are inhibitory themselves, the IN circuits will exert disinhibition of target neurons. Although, regions with predominant inhibitory inputs are exceptional, the number of areas recognized as receiving long range inhibitory projections is increasing, even in the forebrain, suggesting feedforward disinhibitory motifs (FFDM) could be more common than previously assumed. Diversity in inhibitory neurons is assumed to confer flexibility in the control of neural activity. Diversity in IN circuit motifs could represent an additional mode to endow flexibility. FFDM circuits, which have been little studied, may play an important role in this regard. To investigate this hypothesis, the mechanisms and role of FFDM and their interaction with classical inhibitory motifs in shaping neuronal activity need to be further elucidated. Here we propose to investigate this issue in the deep cerebellar nuclei (DCN), the output stage of the cerebellum, which contains glutamatergic, GABAergic and glycinergic neurons. DCN neurons receive most of the GABAergic Purkinje cells axons and integrate this cerebellar cortex output signal with sensory and context ones carried by collaterals of the excitatory cerebellar mossy and climbing fibers. These network characteristics, previous evidence, and our preliminary experimental results suggest the DCN contain FFDMs and classical inhibitory motifs. Together with evidence of limited number of DCN IN classes, DCN appear as a well suited region for addressing the question of how diverse IN motifs shape neural activity. Here we propose to use single and paired whole cell patch (WCP) recordings of DCN neurons in cerebellar slices expressing/lacking fluorophores and/or opsins under the control of specific promoters, combined with intracellular labeling, morphological reconstruction and immunocytochemistry, electrical and optogenetic activation of DCN inputs or specific DCN neuron groups, and calcium imaging, to 1) reliably segment/identify recorded DCN neurons 2) elucidate the blueprints of the DCN IN motifs and points of interaction, and, 2) asses their role by analyzing the intrinsic and synaptic properties of their INs, input and output pathways. With these investigations, we expect to gain insight into the not yet understood organization and function of DCN-IN-circuits, provide the basis for the study of their function under physiological patterns of activity and address the general question of whether and how diversity in the type of IN motifs adds further flexibility to the control of neuronal activity.

• DFG Programme: Research Grants